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The extension pipe combines thee exhaust gas from the turbo and the bypassed gas from the actuator. When the actuator is activated and the gases are forced into one chamber, a secondary pocket of high exhaust gas pressure is created causing boost levels to fall and reduce power. HKS Extension kits have been designed to minimise power loss and extract the most from the turbo.

By separating the main and bypass pipes, exhaust gas flow disruption is minimised. Turbochargers which combine main and bypass gasses within the exhaust housing can still benefit from an extension kit as the kit contains a boss which separates main and bypass gasses in the exhaust housing using a bossed flange. The joining point for the two pipes is placed further down the exhaust where exhaust gas pressure is lower to maximise efficiency. Moreover, the main pipe diameter increases soon after the turbo. The expanded area minimises exhaust gas rotation which can cause exhaust gas pressure increase and reduce power. All these areas reduce exhaust gas pressure build up and provide more power with stable boost levels. Flanges are made from Stainless steel grade which is highly resistant to heat, whilst the pipes are made from SUS304 grade stainless steel for durability, heat resistance and attractive appearance.

View Extension application charts  


The purpose of the extension on swing valve type turbo systems is to smoothly flow exhaust gas from the turbo to the front pipe. This prevents exhaust gas build up reducing load on the turbo to allow the turbo to respond and boost at full capacity. HKS GT Extension kits combine a specially designed extension and front pipe to maximise exhaust gas flow after the turbo. In some applications, the flange between the extension and front pipe is enlarged to allow great gas flow which is only possible through a kit which was specifically designed for this purpose.

For Lancer Evolution

HKS GT Extension kits for Lancer Evolution models replace exhaust piping between the stock turbo and catalyser. The extension section has 60mm diameter main pipe with 58mm bypass pipe which is kept independent from the main pipe to reduce exhaust gas pressure build up close to the turbo. The gases will flow through to a 70mm diameter front pipe. This configuration will make power outputs of approximately 300kW (400PS) possible. Boost response is also improved by approximately 15% over the stock exhaust parts.

For Silvia
  • HKS GT Extension kit gives a wider range of performance options on your Silvia/180SX/200SX. Whether you are using stock turbo, GT-SS or GT-RS, maximum performance can be extracted from your turbo with the GT Extension kit

  • Extension pipe diameters have been increased for both the main and bypass pipes. Boost response is improved by up to 10% and mid/high RPM power and torque is substantially increased over competitors products during tests at HKS Headquarters in Japan.

  • A specially designed dual layout is used for the front pipe. This allows for larger pipe cross sectional area and therefore increased exhaust efficiency. Compared with conventional front pipe designs, the dual layout gives an additional 15-20mm of ground clearance for lowered vehicles.
Model Model Code Engine Code Model Year Pipe Dia* (Main) Pipe Dia* (Bypass) Pipe Dia* (Front) Part Number Retail Price (+VAT) Remarks
SILVIA / 200SX S15, S14   SR20DET   93/10-02/08   φ65   φ50   φ60x2   14018-
621.50 Stock heat insulator must be removed/modified for fitment. Made from SUS304.
LANCER EVOLUTION CZ4A (X)   4B11   07/10-   φ62   φ   φ65   14019-
615.00 Twin Port Spec. Comes with Sensor Boss
LANCER EVOLUTION CT9A(VII, VIII, IX)   4G63   01/02-   φ60   φ58   φ70   14018-
621.50 Unconfirmed for GT-A and MR models. Made from SUS304
LANCER EVOLUTION CN9A, CP9A(IV, V, VI) 4G63   96/08-01/01   φ60   φ58   φ70   1418-
Dia* - Diameter    

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